Asthma is an inflammatory lung disease that affects >300 million people worldwide. Obesity/metabolic dysfunction, which affect 40% of adults in the US, is associated with a more severe asthma endotype. Unlike mild asthma which is driven by a Th2 immune response, the “obese asthma” endotype is associated with frequent asthma exacerbations, a shift away from Th2-dominated inflammation towards a Th17-dominated profile, and a marked female bias. A major gap in our understanding of mechanisms driving the “obese asthma” endotype is due to deficiencies in common mouse models of obesity. Standard mouse models of high-fat diet (HFD) driven obesity are unable to induce extensive weight gain and metabolic dysfunction in female mice - a major shortcoming given the female bias of the “obese asthma“ endotype. Our group has uncovered that HFD feeding of C57BL/6 mice housed at a temperature in which they are at metabolic homeostasis (thermoneutral temperature (TN); 30-33°C) promotes severe obesity and metabolic dysfunction in female mice. Preliminary data using this model demonstrate that allergen-challenged obese female mice exhibit: (1) worse asthma outcomes compared to lean controls; (2) reduced markers of type 2 immunity (eosinophilia, Th2 cytokine production); and (3) a selective increase in the IL-17A production by innate lymphocytes, particularly gd T cells and Mucosal Associated Invariant T cells (MAIT cells). Critically, none of these changes are observed in obese asthmatic male mice. Although both gd T cells and MAIT cells have been ascribed protective roles in the context of asthma and metabolic homeostasis, in obesity their proinflammatory vigor increases, and they become important mediators of glucose intolerance, insulin resistance, and tissue inflammation invoking extreme functional plasticity. Importantly, no studies have examined the role of these cells in obese asthma to date. Based on our novel preliminary data, we hypothesize that, innate lymphoid populations (gd T cells, MAIT cells) acquire pathogenic functions in obese female mice and contribute to the development of the “obese asthma” endotype. This hypothesis will be tested in two aims. Aim 1: To determine if gd T cells or MAIT are necessary and sufficient to trigger more severe asthma in obese female mice. Using gd T cell or MAIT cell blocking agents, and adoptive transfer of purified gd T cell/MAIT populations from lean or obese asthmatic females to lean asthmatic male and female mice, followed by assessment of asthma and metabolic endpoints, we will determine the necessity and sufficiency of these cells in obese asthma. Aim 2: To compare the proinflammatory and metabolic landscapes of innate lymphocytes from lean and obese asthmatic female mice. Transcriptional landscape of purified lung innate lymphocyte populations (gd T cells, MAIT cells, ILCs, iNKT T cells) from lean and obese asthmatic female mice will be analyzed. Changes in inflammatory and metabolic pathway gene expression will...